Filter band multi-carrier modulation is a multi-carrier technology whose primary characteristic is that its subcarrier spectrum in the frequency domain may be designed and controlled flexibly such that it may properly suppress the out-of-band spectrum. The main manner for implementing FBMC is OQAM (offset QAM), that is, the real part and imaginary part of a complex constellation modulation symbol are separated so as to modulate respective pulse signals at a real and imaginary part interval in the time domain and frequency domain. Since the pulse signals have good energy concentration in both the time domain and the frequency domain, compared with the existing OFDM system, it may efficiently reduce the ICI/ISI influence without inserting any cyclic-prefix so that the FBMC system has higher spectral efficiency than the OFDM system. Meanwhile, each subcarrier spectrum decays fast, which facilitates reduction of the out-of-band radiation and improvement of spectrum perception accuracy. Therefore, the FBMC system is especially suitable for future-oriented wireless communication application such as cognitive radio, etc.
In contrast to the existing OFDM system capable of providing complex orthogonality, FBMC may only provide the orthogonality for the real part, which results in intrinsic interface on the imaginary part. The intrinsic interference on the imaginary part in the FBMC system becomes a fundamental issue to be faced and solved in system implementation, especially for the design of the pilot symbols in signal transmission and the corresponding channel estimation methods.
The most popular existing FBMC channel estimation method is the Interference Approximation Method (IAM for short). In the IAM method, the intrinsic interference on the imaginary part is approximated by mainly using a special pilot preamble symbol (as shown in FIG. 1), and then an equivalent virtual complex pilot is constituted by using the real part of the pilot and the approximated intrinsic interference on the imaginary part so as to obtain corresponding channel estimation results.
The main problem of the IAM method is that as shown in FIG. 1, the pilot preamble symbol used by IAM needs to occupy at least 3 FBMC modulation symbols (two FBMC modulation symbols are equivalent to one OFDM modulation symbol), and this pilot overhead greatly reduces the spectral efficiency of the system, and to some extent even partially counteracts the benefit of the FBMC system over the existing OFDM system.
Hence, a new method for designing pilot preamble symbols for signal transmission in the FBMC system and corresponding channel estimation methods is needed.